Arctic Ice's Hardiness Measured with Earthquake Monitors

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Humans have gotten pretty good at monitoring Arctic sea ice with
from afar. Since the end of the Reagan era, watchful satellites
have measured the reach of the ice cover that marches across
Arctic seas each winter and recedes each spring.

And since satellites started sending data back in 1979,
scientists have watched the total area of
annual ice cover steadily decline. The observation has piqued
a flurry of interest in what the future holds for the Arctic and
its disappearing ice — one of the loudest signals of global
climate change.

"Satellite measurements are very good at telling you what
percentage of the area is covered with sea ice," said Victor C.
Tsai, an assistant professor of geophysics at Caltech.

Yet satellites have their limitations, said Tsai, who found that
by looking at data from seismic stations — suites of instruments
best known for measuring earthquakes — scientists can learn
about the
quality of sea ice.

"We think we can measure something to do with how strong the ice
is," he told OurAmazingPlanet. "In order to make
predictions about the future, you need to know the strength of
the sea ice, and not just what percentage is covered."

Seismic sea ice signal

Like many discoveries, this one came as something of an accident.
Tsai was examining data from seismic stations to be sure they
were functioning properly, when he noticed something strange in
the numbers from two stations near the
Bering Sea.

"There was a lack of energy from about December though May," he
said, a time when most seismic stations in northern climes
usually pick up lots of energy — or ground shaking — because
winter storms whip up waves that pound Arctic shorelines.

At first he and his collaborators thought the stations were
malfunctioning, but the numbers revealed the same pattern, year
after year.

"We tried to understand why that was, and we saw, oh yeah, this
ties into when you have significant sea ice around those
stations," he said. Which made sense, since it's known that sea
ice dampens the vigor of ocean waves.

After further investigation, Tsai found a way to mathematically
link the seismic data with how packed or broken up the ice is.
The research was published in the Nov. 19, 2011 issue ofthe
journal Geophysical Research Letters.

Short and long term

Tsai emphasized that the methodology is still young, and he's
working to fine-tune the math. In addition, a larger network of
seismic stations would be required to cover more of the polar
regions and make projections of
how sea ice might fare in the future, an important part of
climate change forecasts.

"Right now we're much better poised to make shorter predictions —
the next week or two — and it's much more difficult to make
predictions for the more distant future," Tsai said.